The present invention relates generally to the installation and renovation of subterranean conduits, and, more particularly, to the grouting or backfilling of such conduits where an annular space in or around the conduit is contaminated or flooded with water.
The installation and renovation of underground conduits frequently requires the placement of cementitious materials to stabilize the conduit. Two exemplary categories of such work to which the present invention pertains (but is not limited) are (i) tunnel backfill grouting, and (ii) slipliner grouting. These two types of grouting are quite different in a number of respects, but they share related problems stemming from the presence of water in the voids which are to be filled with the grout.
Usually considered to be the less difficult of these two types of grouting, tunnel backfill grouting involves filling the space between a conduit and the surrounding geological formation, usually (but not always) in a new installation. For example, in constructing a tunnel a bore is formed through the subterranean formation and a concrete liner is installed in this to form the tunnel itself, for containing and transporting water, traffic, etc. in a protected environment. To stabilize and support the tunnel liner, a fill material is ordinarily placed in the annular space between the liner and the wall of the bore, and for most installations a cementitious mixture is considered to be most satisfactory for this purpose. For the purpose of this invention, the term xe2x80x9ctunnel backfillxe2x80x9d includes not only this type of construction, where a large-diameter (often segmental) liner is installed in a new or previously unlined subterranean bore, but also other installations where the liner is a rigid member which is able to carry a substantial external load, such as a steel or heavy gauge fiberglass liner installed in a new excavation or an old bore/pipe, to give just a few examples.
Slipliner grouting, in turn, is often somewhat more complicated from a technical standpoint, due to the comparative delicacy of the liners which are ordinarily used in this kind of work. In sliplining, an existing, deteriorated conduit (a deteriorated concrete sewer line, for example) is renovated by installing a new liner in the existing pipe. In order to minimize the reduction and flow capacity, the thickness of the liner and also the annular gap between the liner and the pipe must be kept to a minimum. For example, slipliner installations often employ a comparatively thin high-density polyethylene (HDPE) liner with only an 1-3 inch clearance between the outside of the liner and the old pipe. The grout materialxe2x80x94usually cementitious groutxe2x80x94is installed by flowing this through this narrow annulus, but injection pressures must be kept quite low (e.g., below 3 psi in the case of typical HDPE liners): excessive grout injection pressures will tend to collapse the liner, with disastrous consequences for the job. Moreover, it is important that the density of the grout not be so high as to cause the liner to xe2x80x9cfloatxe2x80x9d to the top of the old pipe or other conduit, since this again will tend to cause the liner to collapse during grouting, and also exposes the liner to external pressures exerted by the surrounding geological formation in those areas where the original pipe/conduit has been penetrated by erosion or has failed structurally.
As was noted above fluid cementitious materials are generally used as the grout materials for both tunnel backfill and slipliner grouting. A category of cementitious grout materials which is particularity useful in both tunnel backfill grouting and slipliner grouting consists of cellular cement grouts, in which an aqueous finished foam material is added to a cement slurry to entrain large amounts of air in the grout; an example of such a foamed cement grout for use in sliplining is provided in U.S. Pat. No. 5,063,967, the inventor of which is the same as in the present matter. Such cellular cement grouts have significant economic advantages for both tunnel backfill and slipliner grouting, since the large volumes of entrained air reduce the amount of Portland cement which is required to complete the fill. Moreover, in the case of slipliner grouting, the use of foamed cement grouts permits the density of the grout to be kept low enough to prevent the liner from floating (when the latter is kept full or partially full of water), and the fluidity of the material permits it to be injected lengthwise through the annulus over long distances without developing excessive injection pressures which might collapse the liner.
Although cellular cement grouts are thus highly advantageous for tunnel backfill and slipliner grouting, in both cases the use of this material can become extremely difficult where the annular space (i.e., the space between either the tunnel liner and bore or the slipliner and original pipe) is flooded or otherwise contains large amounts of water. This is a very common situation, due to eboth the intrusion of naturally-occurring underground water and also because in many cases (especially in sliplining work) it is not feasible to completely evacuate or stop the flow of water through the conduit or through adjacent conduits which are in communications with the conduit which is being worked on, such as is often the situation with municipal sewer lines.
The presence of large amounts of water (often moving) in the-annulus plays havoc with the grouting process. To begin with, the water tends to cause excessive xe2x80x9cwashoutxe2x80x9d of the cement fines, leading to unacceptable losses in effective yield (i.e., excessive grout material is required in order to fill the cavity), and also to severe loss of compressive strength in the cured installation. Moreover, when using cellular cement grouts, the water tends to cause stratification in the grout material and collapse of the bubble-structure, so that the bubbles migrate to the top of the annulus and the cement slurry to the bottom. The collapse of the bubble structure leads to an even more severe loss in effective yield, and, in the case of the slipliner grouting, the accumulation of heavy slurry material in the bottom of the annulus tends to float the liner to the top of the old pipe/conduit, leading to possible collapse and the other kinds of problems described above.
In the case of tunnel backfill grouting, there have been some limited attempts at overcoming these problems in the past, however none of these has proven truly successful in practice. The relevant prior art of which Applicant is aware at the time of this application includes U.S. Pat. No. 4,419,135 (Hoge), in which an effort was made to deal with the problem of ground water in tunnel backfill situations by adding a superplasticizer and pituitous polyethylene oxide water thickening agent to a foamed concrete grout mixture. In practice, this material has been found unsuitable in a number of respects. Firstly, it has been found difficult or impossible to produce a stable, homogenous mixture using the Hoge composition, with the material tending to separate into long, xe2x80x9cgooeyxe2x80x9d strings which cannot be pumped or worked with effectively, and which are not satisfactory from the standpoint of quality control and final compressive strength. Furthermore, it is difficult or impossible to flow or pump the Hoge composition over any significant distance through an annulus; the examples given in the Hoge patent generally show the material simply being dumped into the cavity (xe2x80x9cfree-fallxe2x80x9d installation) rather than being pumped, and the longest distance which the material is shown to flow through a tunnel is 850 lineal feet xe2x80x9cbefore the flow rate fell to zero.xe2x80x9d In modern tunneling installations, the grout must be able to flow not hundreds but thousands of feet through the annulus, or else access points (e.g., drill holes) must be provided from either the surface or the interior of the tunnel at many points along its length to permit sequential grouting, at great cost. Still further (although the reference does not suggest its use for this purpose), the Hoge composition would develop excessive back pressures if one were to attempt to use this for slipliner grouting, which would cause the liner to collapse almost immediately.
Accordingly, there exists a need for a method and composition for grouting annular spaces in underground conduits which are flooded or heavily contaminated with water, which eliminates the problem of washout of the cementitious fines in a foamed cement grout and the resultant loss of yield. Still further, there is the need for such a method and composition in which the presence of water will not cause segregation of the grout components and collapse of the bubble structure. Still further, there exists a need for such a method and composition in which a foamed cement grout will maintain a stable, homogenous mixture, and in which the grout is highly fluid and can be pumped into an annulus over very long distances (i.e., distances well in excess of 1,000 lineal feet) without the flow rate reaching zero. Still further, there is a need for such a method and composition in which the cellular cement grout is sufficiently fluid that low injection pressures can be maintained so as to avoid collapse of a slipliner in slipliner grouting, and in which the density of the grout can be kept sufficiently low to avoid the grout causing a water-containing slipliner to float to the top of the annulus.
The present invention has solved the problems cited above, and is a method and composition for the grouting of water-flooded annular spaces.
Broadly, the method comprises the steps of: (1) combining hydraulic cement and water in predetermined amounts to form a fluid cement slurry, (2) colloidally mixing the cement slurry so as to achieve ultra-fine mixing thereof, (3) adding a liquid anti-washout admixture to the slurry in a predetermined amount, (4) adding finished foam to the slurry in a predtermined amount after the colloidal mixing and after addition of the anti-washout admixture, so as to form a stable foamed cement grout, and (5) injecting the foamed cement grout into the annular cavity.
The method may further comprise the step of adding superplasticizer to the slurry in a predetermined amount.
The cement used in the present invention is neat cement which is substantially free of sand or any other aggregates. The anti-washout agent is preferably a modified cellulose ether solution which is substantially free of any anti-foaming agents.
The water-to-cement ratio of the grout can be in the range from about 0.4-1.0, and the unit weight of the grout after addition of the finished foam can be in the range from about 40-90 pcf, with 50-75 pcf being preferable for the majority of applications.
The anti-washout agent noted above is preferably added at a metered rate in the range from about 5-20 ounces per hundredweight of cement, with a range of about 8-12 ounces per hundredweight of cement being preferable for the majority of applications.